For

Against

When the Jaguar XKR-S coupe emerged last year, it proved to be the the company’s fastest, most powerful mass produced vehicle ever. It was undoubtedly brilliant, but to sun-worshipping petrol-heads it was horribly flawed in one respect - it had a roof. Thankfully, Jaguar has taken to the XKR-S coupe with a large hammer and replaced its metal roof with an electrically retracting soft top to create the new XKR-S convertible.

Elated, we splashed on some sunscreen, donned our Aviator shades and headed to southern California to see how it compares to its be-roofed predecessor.

Looks like a looker

Apart from the gaping hole where the lid used to be, the XKR-S convertible is virtually identical to the XKR-S coupe. In other words, it has a sleek, athletic body that has been festooned with several aerodynamic accoutrements. These include a carbon spoiler at the front, a large Mustang-esque wing, mounted on the boot and side skirts running the length of the car. Together, these components work like a plane’s wings, except in reverse, helping to reduce the chances of the car taking off at high speed.

Flash! It’ll save every one of us

Climb inside the Jaguar XKR-S, and you may find yourself slightly underwhelmed by the car’s interior. There’s nothing overtly wrong with it - it’s just that it’s interior furnishings don’t quite live up to to the billing of its lust-worthy exterior.

That said, the car features some relatively impressive cabin tech. The centrepiece is a 7-inch touchscreen display that provides access to the majority of the car’s geekier functions. It’s a joy to use, and the menu system is arguably the most logically arranged we’ve come across, even if its interface is based on the increasingly out-of-favour Macromedia Flash.

Running vertically across the left side of the display, there are five tabs that give you access to audio, climate, phone, navigation and vehicle functions. Prod one of these and you’ll be taken into a sub-menu that allows you to tinker with settings for whatever option you’ve just selected. If you get lost or bewildered in some way, which is pretty difficult to do, you can always hop back to the main menu by hitting the physical "home" button located below and to the right of the screen.

Yesterday’s news

Although it’s easy to use, Jaguar’s information and entertainment package is beginning to show its age. The Jag’s cabin tech, unlike rival systems from the likes of BMW, Audi and Mercedes-Benz, isn’t connected to the wider world, via the internet. As a result, it lacks the ability to send and receive rich, up-to-date information on demand.

It's sat-nav, for example, doesn’t follow the new trend of using Google local search to hunt down points of interest, nor does it help you avoid jams using real-time traffic information. There’s no Twitter or Facebook integration and you can’t upgrade its functionality by downloading apps.

That said, the XKR-S convertible redeems itself with a truly sensational Bowers & Wilkins audio system. Even with the roof down, the it’s loud, clear, and the subwoofers can be cranked up to a level that makes you feel as if you’re being kicked in the kidneys - in a good way. It is, without question, the best factory-fitted audio system we’ve encountered in any convertible car.

There’s decent support for audio sources, too. It’ll play AM, FM and DAB radio, CDs, stream tunes from a mobile phone via Bluetooth and blast songs from your iPod or a USB stick. There’s no integrated hard drives or internet radio shenanigans going on in this bad boy, but that hardly matters given the incredible sound this car makes when you fire it up.

Sound thinking

Push the button on the dashboard labelled "start" and the XKR-S will serenade you with a superior form of aural pleasure. One prod from a fleshy index figure triggers a banshee-like staccato from beneath the bonnet, immediately followed by a low, guttural bark from its exhaust, before the revs fall and the whole thing settles to a low rumble.

The engine, the cause of all this beautiful racket, is the same 5-litre supercharged unit found in the slightly less bonkers XKR. However in the XKR-S convertible, it’s mated to a new, free-breathing exhaust system that adds bucketloads of power - and noise. Naughtily, Jaguar’s removed one of the resonators that helps keep the exhaust quiet and fitted an x-shaped segment that reduces pressure, helping the whole thing breathe more freely. Not only do these changes make the exhaust note more dramatic, they also have a significant effect on power output -- the 500bhp output of the XKR becomes a heady 542bhp in the XKR-S.

Performance of a lifetime

With all that grunt, it’ll come as no surprise to learn the XKR-S is fast. Mash the accelerator pedal into the carpet and the thing takes off like like a panicked horse, leaping towards the horizon with relentless urgency. It’ll conquer the 0-60mph sprint in 4.2 seconds, but what’s most impressive is the fact this obscene talent for acceleration can be summoned on a whim, no matter what speed you’re doing. If you need a sudden, tidal wave of thrust, the XKR-S will deliver it, no questions asked.

It’s incredibly composed at speed, too. We managed to get near the car’s 186mph terminal velocity with the top down and it felt remarkably composed, even with crosswinds doing their best to unsettle it.

It’s not shy when faced with a few corners, either. Most convertibles suffer a loss of torsional rigidity and a decrease in handling prowess owing to their lack of a roof. They waddle their twisting bodies through bends and bumpy roads, feeling as if they’re made of damp socks, but the XKR-S feels solid and coupe-like. It remains stable when changing direction rapidly, its steering feels as precise as the coupe’s and it inspires confidence at every speed.

Thirsty work

The one major drawback of this car’s exquisite performance is its thirst and general disdain for Mother Nature. It drinks fuel at a rate of 23mpg on the combined cycle, and spews 292g of carbon dioxide per kilometre, which is pretty poor - even by supercar standards. Porsche, by comparison, says its (marginally less bonkers) 911 Carrera S cabriolet will achieve 29.1mpg combined and emits CO2 at a rate of 229g/km.

Verdict

The XKR-S convertible is brilliant in almost every way. Its incredibly powerful engine and raucous exhaust help it deliver the sort of performance that can put rivals from Aston Martin and Porsche to shame. It is stupendously quick in a straight line and capable of accelerating to the sorts of license-ruining speeds usually reserved for aircraft.

However it's also surprisingly agile. The laws of physics says it should never be as quick as its coupe sibling, but ordinary mortals are likely to discover the limits of their driving ability before they approach the limit of the mighty Jag.

If your wallet can withstand the impact of the price tag and the subsequent running costs, we think you’ll find this is a truly world class convertible sports car that will give you an endless supply of power and joy every second you’re behind the wheel.